1. Field of the Invention
This invention relates to a hydraulic braking system for a motor vehicle and more particularly to an anti-skid unit incorporatable therein.
2. Description of the Prior Art
As is well known, it is desirable in view of the ever increasing performance capabilities of the modern motor vehicle to provide therein an anti-skid device or unit which will prevent excessive pressure being fed to the cylinders of the brake units during sudden deceleration and thus prevent dangerous wheel lock up and resulting skidding of the vehicle. This is particularly so in modern motor vehicles wherein efforts are being constantly made to reduce the overall weight and complexity of the vehicle components and thus the vehicle, so as to reduce the consumption of dwindling petroleum supplies.
One particular anti-skid unit is activatable by a computing circuit which temporarily cuts or severely limits the communication between the master cylinder of the braking system and the brake units and simultaneously expands the pressurized hydraulic pressure entrapped in the brake unit cylinders to reduce the braking effect generated thereby. This operation is repeatable to maintain the rate of deceleration below a predetermined safe level. However this unit has suffered from overcomplexity and excessive weight in that it uses three spool type valves or valve units slidably disposed in three separately formed stepped bores. The resulting conduiting required to interconnect the three bores presents many locations requiring sealing and is difficult to machine and produce during manufacture of same. Furthermore a rather large heavy bulky housing is required to house the three valve units thus incurring the aforementioned weight penalty.